Why it makes sense for Google to buy YouTube

The number one threat to YouTube has always been the possibility that they will be sued out of existence because of users uploading copyrighted videos. The theory is YouTube hasn’t been sued yet because they have no money. However, if a buyer with a big bank account comes along, watch the lawsuits fly. This argument doesn’t hold much water. Google has tons of copyrighted materials on Google Video. Google has tons of cash. Where are the lawsuits?